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Handle some simple cases where we can see that values get annihilated. 

llvm-svn: 21771
This commit is contained in:
Chris Lattner 2005-05-08 00:08:33 +00:00
parent 4294cec0f1
commit 6e2086d7e4
1 changed files with 42 additions and 7 deletions
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49
llvm/lib/Transforms/Scalar/Reassociate.cpp
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@ -113,10 +113,16 @@ unsigned Reassociate::getRank(Value *V) {
i != e && Rank != MaxRank; ++i)
Rank = std::max(Rank, getRank(I->getOperand(i)));
// If this is a not or neg instruction, do not count it for rank. This
// assures us that X and ~X will have the same rank.
if (!I->getType()->isIntegral() ||
(!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
++Rank;
DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
<< Rank+1 << "\n");
<< Rank << "\n");
return CachedRank = Rank+1;
return CachedRank = Rank;
}
/// isReassociableOp - Return true if V is an instruction of the specified
@ -388,11 +394,40 @@ void Reassociate::ReassociateBB(BasicBlock *BB) {
goto FoldConstants;
}
// FIXME: Handle destructive annihilation here. Ensure RANK(neg(x)) ==
// RANK(x) [and not]. Handle case when Cst = 0 and op = AND f.e.
// FIXME: Handle +0,*1,&~0,... at end of the list.
// Check for destructive annihilation due to a constant being used.
if (Ops.size() != 1) { // Nothing to annihilate?
if (ConstantIntegral *CstVal = dyn_cast<ConstantIntegral>(Ops.back().Op))
switch (I->getOpcode()) {
default: break;
case Instruction::And:
if (CstVal->isNullValue()) { // ... & 0 -> 0
Ops[0].Op = CstVal;
Ops.erase(Ops.begin()+1, Ops.end());
} else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
Ops.pop_back();
}
break;
case Instruction::Mul:
if (CstVal->isNullValue()) { // ... * 0 -> 0
Ops[0].Op = CstVal;
Ops.erase(Ops.begin()+1, Ops.end());
} else if (cast<ConstantInt>(CstVal)->getRawValue() == 1) {
Ops.pop_back(); // ... * 1 -> ...
}
break;
case Instruction::Or:
if (CstVal->isAllOnesValue()) { // ... | -1 -> -1
Ops[0].Op = CstVal;
Ops.erase(Ops.begin()+1, Ops.end());
}
// FALLTHROUGH!
case Instruction::Add:
case Instruction::Xor:
if (CstVal->isNullValue()) // ... [|^+] 0 -> ...
Ops.pop_back();
break;
}
}
if (Ops.size() == 1) {
// This expression tree simplified to something that isn't a tree,